The disclosure relates to coated particles and to methods for making and using the same. In particular, this disclosure relates to coated particles that are used as proppants or in gravel packs.
Coated and/or uncoated particles are often used as proppants to keep open fractures imposed by hydraulic fracturing upon a subterranean formation, e.g., an oil or gas bearing strata. Proppants are generally used to increase production of oil and/or gas by providing a conductive channel in the formation. Fracturing of the subterranean formation is conducted to increase oil and/or gas production. Fracturing is caused by injecting a viscous fracturing fluid or a foam at a high pressure (hereinafter injection pressure) into the well to form a fracture. As the fracture is formed, a particulate material, referred to as a “propping agent” or “proppant” is placed in the formation to maintain the fracture in a propped condition when the injection pressure is released. As the fracture forms, the proppants are carried into the fracture by suspending them in additional fluid or foam to fill the fracture with a slurry of proppant in the fluid or foam. Upon release of the pressure, the proppants form a pack that serves to hold open the fractures. The propped fracture thus provides a highly conductive channel in the formation. The degree of stimulation afforded by the hydraulic fracture treatment is largely dependent upon formation parameters, the fracture's permeability and the fracture's propped width.
Coated and/or uncoated particles can also be used as gravel packs. An example of a well completion operation using a treating fluid that contains coated particulates is gravel packing. Gravel packing treatments are used to reduce the migration of unconsolidated formation sands into the well bore. In gravel packing operations, the particles suspended in a carrier fluid are pumped into a well bore in which the gravel pack is to be placed. The carrier fluid leaks off into the subterranean zone and/or is returned to the surface while the particles are left in the subterranean zone. The resultant gravel pack acts as a filter to separate formation sands from produced fluids while permitting the produced oil and/or gas to flow into the well bore.
Gravel pack operations generally involve placing a gravel pack screen in the well bore and packing the surrounding annulus between the screen and the well bore with the particles. The gravel pack screen is generally a type of filter assembly used to support and retain the particles placed during the gravel pack operation. A wide range of sizes and screen configurations are available to suit the characteristics of a particular well bore, the production fluid, and the subterranean formation sands. Such gravel packs may be used to stabilize the formation while causing minimal impairment to well productivity. The particles act to prevent formation sands from plugging the screen or migrating with the produced fluids, and the screen acts to prevent fines from being produced to the surface and out of the well.
In some situations the processes of hydraulic fracturing and gravel packing are combined into a single treatment to provide stimulated production and an annular gravel pack to reduce formation sand production. Such treatments are often referred to as “frac pack” operations. In some cases, the treatments are completed with a gravel pack screen assembly in place, and the hydraulic fracturing treatment being pumped through the annular space between the casing and screen. In such a situation, the hydraulic fracturing treatment usually ends in a screen out condition creating an annular gravel pack between the screen and casing. This allows both the hydraulic fracturing treatment and gravel pack to be placed in a single operation.
Particles that are used to prop fractures or in gravel packs generally comprise sand or sintered ceramic particles. The advantage of sand is that it is inexpensive. Its disadvantages are its relatively low strength (high crush values) and lower flow capacities than sintered ceramic particles. Sintered ceramic particles are also used as proppants or in gravel packs. The ceramic particles are disadvantageous in that the sintering is carried out at high temperatures, resulting in high energy costs. In addition, expensive raw materials are used. They have relatively high bulk densities of greater than 2 grams per cubic centimeter (g/cm3), and have abrasive properties that cause high wear in the pumps and lines used to introduce them into the drill hole.
It is therefore desirable to develop particles that can be used for hydraulic fracturing and/or gravel packs and are cost effective, have a density of less than 2 g/cm3, reduce the formation of fines, and can be easily manufactured.